Use of packet-switched connections for transmitting synchronous communications, such as voice calls, and data across telecommunications networks is increasing. Such packet-switched connections allow for greater speed and throughput than do circuit-switched connections, and also make packet-switched data from other networks, such as the Internet, more readily available. Most telecommunications networks, however, still utilize access networks that provide circuit-switched connections, such as Global System for Mobile Communications (GSM) networks or Universal Mobile Telecommunications System (UMTS) networks, due to the substantial infrastructure investment needed to expand packet-switched access networks. Such circuit-switched access networks may provide comparable or, at times, better speed and quality than packet-switched access networks for some types of data, including synchronous communications such as full-duplex voice communications.
Because packet-switched access networks are not available to the same extent as circuit-switched access networks, techniques have been developed for switching from one of type of packet-switched access network—e.g., the Long Term Evolution (LTE) access network—to circuit-switched access networks while maintaining continuity for a communication session, such as a voice call. An example of a communication session is an emergency call from a user to a Public Safety Answering Point (PSAP).
One technique for handover of a communication session from a LTE access network to a circuit-switched access network involves the use of the single radio voice call continuity (SRVCC) standard produced by the Third Generation Partnership Project (3GPP). With SRVCC, an eNodeB of a LTE access network determines that a communication session handover should occur based on a measurement report received from user equipment. The eNodeB communicates this to a mobility management entity (MME), which makes a handover request of a mobile switching center (MSC) server of a circuit-switched access network that is available to the user equipment. The MSC server (MSS) then prepares the circuit-switched access network for the handover, and communicates with an Internet Protocol (IP) multimedia subsystem (IMS) of the telecommunications network, the IMS maintaining continuity for the communication session during the handover. The MSS then sends a handover response to the MME, and the MME instructs the user equipment to connect to the circuit-switched access network to continue the communication session.